This invention relates to a sacrificial anode for marine propulsion units, and more particularly to the placement and construction of a sacrificial anode mounted to a marine stern drive, outboard motor, or the like for purposes of protecting the parts of the unit against corrosion.
Sacrificial anodes of zinc or the like have long been utilized in marine applications for protecting the metallic parts of aluminum or the line in marine applications. Heretofore, such anodes have been positioned in numerous places. They have often been placed on the bottom or side of a marine vehicle itself. More frequently, however, they have been positioned directly on the propulsion unit. In the past, the placement has usually been below the anti-cavitation plate in the lower area of the drive unit, and has taken the form of a so-called trim tab depending downwardly from the plate. Such placement has done little to cathodically protect the upper portion of a drive unit.
Consideration has been given to providing better protection for the upper drive shaft housing by placing a sacrificial anode above the anti-cavitation plate. Various placements have been considered, and one has been adopted forwardly of the vertical drive housing adjacent the transom, but this does not protect the rearward upper portion of the unit. Aesthetics and the inability to provide sufficient weight or surface area of the anode to be truly effective are still problems. One of the major problems has been to find adequate space for the anode adjacent the rearward portion of the upper drive shaft housing, in view of the complex and tightly crowded various structures required in that area.
It is an object of the present invention to solve the aforementioned problems, and to position a sacrificial anode adjacent the upper drive shaft housing of a marine propulsion unit, while not interfering with the other adjacent mechanisms. It is a further object to provide such an anode which is aesthetically acceptable, and which has sufficient weight and surface area to be highly effective.
The present invention is based on a unique solution to the said problems. It has been noted by the present inventor that in marine propulsion systems utilizing trim cylinders for pivotally raising and lowering the drive unit, the piston rod of the trim cylinder has extended rearwardly beyond the cylinder itself by several inches before the rod terminates in a rodeye or other member which is pivotally mounted to an aft portion of the upper portion of the drive shaft housing. The resultant space between the cylinder and rodeye has previously been unused.
Broadly in accordance with the various aspects of the invention, a sacrificial anode is disposed in association with the trim cylinder unit and is positioned in the previously unused area between the aft cylinder end and the rodeye or the like on the piston rod end. More specifically, the anode is in the form of an elongated generally cylindrical member of a diameter approximating that of the trim cylinder to provide improved mass characteristics, and is deeply grooved to thus provide ribs which enhance the working surface area. The anode may be attached to an extended pilot member which is suitably secured within the aft end of the trim cylinder. It is contemplated that a cover may be utilized in conjunction with the anode to improve the aesthetic appearance of the affected area, while permitting water flow through the anode.
In one embodiment, a unitary anode is provided with a radial slot, which permits the anode to be positioned over the trim cylinder rod. In another embodiment, the anode is formed as two half cylinders. In yet another embodiment, the anode is formed as two segments, each having staggered puzzle-like configurations which are interfit. Depending on the anode type, the anode may be secured to the pilot member by longitudinal bolts or by a rib and groove connection. Alternately, the anode may be secured directly on the trim cylinder piston rod shaft. In addition, the anode cover may be secured to the anode itself or to the trim cylinder by a snap-on arrangement.